In a conventional process for manufacturing a link plate for a roller chain, a band of sheet steel is intermittently forwarded to, and punched by, a succession of dies. Edges formed in the punching process, including outer peripheral edges of the partially formed link plates, and inner peripheral edges of connecting pin-receiving holes punched in the link plates, are shaved by means of shaving dies to prevent microscopic cracks from forming.
FIGS. 5 and 6 illustrate the process of producing a link plate 500 by the conventional process. Rough punching and shaving are carried out continuously on a band H of sheet steel. Connecting pin holes 510 are formed first, and then, as shown in the enlargement of region B in FIG. 6, the outer periphery 520 of the link plate is formed. When the roller chain is in use, the outer peripheries 520 of the link plates may contact the surface of a chain guide (not shown).
As shown in FIG. 5, the band H of sheet steel is pulled from a supply roll (not shown) and intermittently forwarded into a link plate punching die assembly D, using pilot holes R as references. The connecting pin holes are punched by rough punching dies d1 and shaved by shaving dies s1. Peripheral parts of the link plates are then formed by rough punching dies d2 and shaved by shaving dies s2. After the link plates 500 are punched by and shaved, the remainder of the band H is recovered by being wound onto a take-up roll (not shown). A very slight bending or strain in the widthwise direction, generated as the band is wound onto the supply roll, causes snaking or slanting of the band as it is forwarded through the die assembly. As shown on an enlarged scale in FIG. 6, because of the snaking of the steel band, the roughly punched areas may become displaced laterally by a distance X when they reach the shaving dies S2.
As a result of the lateral displacement due to snaking of the steel band, especially in the case of a small shaving margin, for example a margin of about 0.1 mm, shaving may not be carried as intended. A portion of the edge of the plate being produced may not be shaved, and this will inevitably cause increased wear in the shoe of a chain guide cooperating with the chain. Moreover, in those parts of the edges of the guide plate where shaving is not performed, microscopic cracks are generated. Chain breakage due to the microscopic cracks could not be prevented, and the required chain strength could not be maintained over a long time. Additionally, whereas ring-shaped chips would ordinarily be produced and discharged in the case of perfect alignment between the shaving die and the roughly punched link plate, the punching displacement X causes the chip to be only partially cut off, and the partially cut off chips are not perfectly discharged. Parts of the chips remain on the link plates 500, as flaws, reducing the quality of the link plates.
A further problem encountered in the conventional method of forming chain plates was that the accuracy of the distance between the inner surfaces 510 of the conventional connecting pin holes and the back surface 520 of the plate could not be maintained. Moreover, bending of the steel band H in the link plate punching die assembly D causes variations in the positions of the plate back surfaces relative to the chain travel line, causing accelerated wear of the shoe of a chain guide.
The general objects of the invention are to solve the above-mentioned problems encountered in the prior art, and to provide a method of manufacturing a link plate for a roller chain, which suppresses displacement of the roughly punched link plate relative to the shaving die, even if bending occurs in the steel band as it is forwarded past the link plate punching die. More uniform punching is attained, and the link plate which is produced exhibits excellent finishing accuracy at the surface which contacts the shoe of a chain guide and at the inner surfaces of the connecting pin holes. In the link plate, an accurate right angle relationship of the punched surfaces and the flat surfaces of the plate is maintained, and the punched surfaces are maintained in accurate, parallel relationship to one another.